The present invention relates to treating biomass in order to enhance its value or rank. More particularly, the invention provides a process for the treatment of coal or other biomass to efficiently convert the selected raw feed stock from low rank into a high-grade fuel capable of increased heat release per unit of fuel. This invention is particularly targeted to serve the utility, commercial and industrial markets. It is also very capable of supplying a low smoke fuel for domestic use, such as home heating and cooking use.
Biomass is one of the largest and most readily available energy sources known to man. Biomass is found in immature forms, such as wood, shells, husks and peat. Vast amounts of biomass are also available in the form of lignite, sub-bituminous, bituminous and anthracite coal. Man has been releasing the energy trapped in the aforementioned materials ever since he discovered and was able to master fire. The inefficient release of these vast energy reserves, however, has resulted in a degradation of the quality of the atmosphere and the environment. The increasing demand for energy, created by man""s insatiable appetite for the products made available by an industrialized society, have created a need to release this energy in a safe, clean and environmentally responsible manner.
Prior processes have recognized that heating coal removes the moisture and, as a result, enhances the rank and BTU production of the coal. It is also known that this pyrolysis activity alters the complex hydrocarbons present in coal to a simpler set of hydrocarbons. This molecular transformation results in a more readily combustible coal. Processes have been developed using high temperature (in excess of the coal""s auto-ignition point). This high temperature art requires the control of the atmosphere in which this heated coal is treated in order to eliminate the auto-ignition of the coal. However, these high temperature, atmosphere-controlling devices produce an unstable product. The xe2x80x9cshocked or face powderedxe2x80x9d coal produced in these furnaces created a need to reassemble this treated material into a manufactured form (briquette). Processes were then developed which include grinding of the coal into a material less than {fraction (3/16)}xe2x80x3 (fines). These fines are pyrolized to reduce the moisture and volatile matter, usually at temperatures ranging from 400 F. to 700 F. These fines are then mixed with a binder, which is either inherent or foreign to the process. The resulting mixture is formed into predetermined sized briquettes. The resulting briquettes are low or void of moisture, modestly stable and devolatilized to some degree.
These prior processes require from 2 to 6 hours to complete. They are slow and costly, both in capitalization costs and production costs. A need exists for an improved process for treating coal to increase its rank while reducing the time and cost of completing the process. The present invention seeks to fulfill that need.
It has now been discovered, according to the present invention, that it is possible to treat coal or other biomass under conditions and over a relatively short time period to enhance its rank to produce a fuel of 12,500 to 13,000 BTU/lb content or higher. In accordance with one aspect, the invention provides a process for treating biomass, typically coal, to increase its rank, wherein a biomass feedstock is heated to remove moisture and volatiles from the feedstock, and the treated biomass is thereafter collected. The term xe2x80x9cremove moisturexe2x80x9d as used herein, means that the contents of moisture (water) is reduced to less than 2% by weight. The reduction of volatile material and organic hydrocarbons is a controlled part of the process whereby the time of exposure, the temperature, and the atmospheric conditions are all predicated upon the volatile makeup of the initial feed stock and the desired volatile makeup of the finished product. This finished product can be 25% by weight or greater volatile matter, for example 25-35%, or 3% or less by weight volatile matter, more usually 5-15% by weight. The present invention provides for detailed control over the end result of the raw feed stock with regard to the volatile matter and other characteristics of the final product.
In a further aspect, a portion of the steam and volatiles removed during the heat treatment of the feedstock in a heating means are recycled back into the heating means, along with a predetermined mixture of liquid hydrocarbons, to provide a non-oxidizing atmosphere which will prevent ignition of the feedstock during the heating step. The term xe2x80x9cnon-oxidizing atmospherexe2x80x9d, as used herein with respect to the entire treatment process, means an atmosphere wherein the oxygen content is typically less than 2% oxygen, usually 0.001-1% oxygen, more usually 0.25 to 0.75% oxygen, by volume.
In yet a further aspect there is provided coal of increased rank produced according to the process of the invention.
In yet another aspect, the invention provides briquettes formed from coal treated according to the process of the invention. The briquettes may be provided with a waterproof coating to improve stability, ignition properties and to extend shelf life.
The process of the invention allows for the controlled volatilization and removal of moisture and organic volatiles, while maintaining the majority of the biomass"" natural structural integrity, with reduced disintegration to powder form, thereby converting low grade fuel of, for example, 7500 BTU/lb. or less, into high-grade fuel of 12,500 BTU/lb. or higher. The process greatly reduces capitalization and production costs required to arrive at the desired result, thus substantially increasing the cost effectiveness and production rate over prior processes. This invention also greatly reduces the time necessary to complete the process from the existing processes of hours to 15 minutes or less, more usually 5-10 minutes.